JPS63976B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for encoding messages in digital form, which has particular application in the communications equipment industry.

The invention will be described in relation to the encoding and decoding of audio signals, such as those available for certain subscription (private subscription fee) types of wireless or wire broadcasting. The invention has inherently broader applications and can be used, for example, for the encoding of video signals for subscription (private membership fee) television or for cable television, and also for the encoding of audio signals. It is also useful in the area of satellite communications of signals, video signals and other forms of information, such as data that can be transmitted in digital form. The invention will be described as having a separate decryption key for each receiver. However, the principles disclosed herein are equally applicable to separate decoding keys for each subgroup of receivers. Therefore, the term receiver should be understood to also include small groups of receivers.
The important thing is not to use a common decryption key for more than a few individual subscribers.

The principal object of this invention is to provide two levels of security: a first level of security that provides an encoding of the information bearing signal, and a code or key for decoding the information bearing message in this first level of security. An encoding system of the type described above with a second stage of security used to encode changes in the data.

Another object is an encoding system of the above-mentioned construction in which the second stage security has a separate and independent decoding key for each receiver in the system.

Another object is a coding system of the aforementioned type having a transmitter that periodically broadcasts or transmits information filled with a message in a coded format in a particular key that can be changed periodically. Key changes are themselves encoded by a second key, and each independent receiver of the system has a separate second key.

Other objects will appear in the following description, drawings and claims.

As mentioned above, the two-stage security encoding concept disclosed herein is applicable to a wide variety of communication systems. It is available for satellite communications, subscription television, subscription radio, cable systems and various forms of data communications. The following description may be particularly applicable to encoding digital audio information, but as is clear from the foregoing description, the invention should not be so limited.

Figure 1 shows one source of audio information in digital format.
0, which is connected to a data encoding circuit 12, which is, for example, a Fairchild 9414 as a basic integrated circuit for encoding digitized audio information.
can be used. A source of digital audio information is connected to a data port of encoding circuit 12. A key generator 14 is connected to the key port of encoding circuit 12 and provides keys for use in encoding digital audio information. Therefore,
The output from the encoding circuit 12 is
It is digitized audio information encoded by a specific key called a key.

The output signal from circuit 12 passes to a signal combiner 16 and then to a modulator 18, which modulator is configured for a particular medium, i.e. broadcast or
The information is transmitted in an appropriate form depending on whether it is wired or satellite communication.

As mentioned above, the first key is modified based on certain rules to provide additional security. The key change start circuit is displayed as 20,
This causes key generator 14 to generate a new key. The circuit 20 is programmed to periodically or randomly initiate a new key cycle by generating a new key start signal.
The new key is then added to block 12 for encoding the digitized audio information. The new key start signal is also applied to the address sequence circuit 22, which searches for a valid subscriber address stored in the random access storage of the subscriber database 24. The subscriber list need not be searched in any particular order, as it is important to ensure that each subscriber whose address is still valid is addressed on every key change.

Connected to the subscriber database 24 is a key generator 26, which may be in the form of read-only storage or ROM, and contains a separate and independent key for every subscriber in the entire system. . The output from the key generator 26 is connected to a key encoding circuit 28 which transfers the key from the key generator 26 and its corresponding address from the database 24 to the key encoding circuit 28.
, and its data port receives the new key from key generator 14 .
In this regard, key generator 14 may be any random number generator that generates independent, non-repeatable keys. The new key applied to the data port is encoded by the sequence of keys provided by the key generator 26, so that each message contains the address and the encoded new key, the encoding being This is done in a second key, which is different for each receiver. This message is from circuit 28
and is connected to a signal combiner for subsequent transmission as described above. Therefore, each time there has to be a change in the first key to encode information with a signal, this change in the key itself is encoded in a message, and this message is encoded in the address and the second key. and a first key. This second key is unique to only one receiver.

Referring to the receiver shown in FIG. 2, the information comprising the key change message described in connection with FIG. Given. There are two outputs from demultiplexer 32. One output is labeled the voice channel at 34 and is connected to a data decoding circuit 36 with a data port and a key port.
Encoded information with signals is provided to the data port and the output from data decoding circuit 36 is audio information in usable form.

A specific key available at a specific time, i.e. the first
A storage device 38, such as containing a key, is connected to the key port of the data decoding circuit 36 and provides a means for decoding the encoded information bearing signal. Again, the specific integrated circuit for the data decoding circuitry may be a fairground 9414 suitably connected for decoding.

The second output from demultiplexer 32 is 40
A control channel, shown as , is connected to a first data selection and buffer amplifier circuit 42 and a second similar circuit 44 . Circuit 42 selects the address portion of the control message, and circuit 44 selects the message portion. The circuit 42 is a comparator 46
The address portion of the message is compared with the hardwired address in ROM 48 in this comparator. Assuming a valid comparison exists and the message is for that particular receiver, comparator 46 to gate 50 and random access memory (RAM) 5
There is an output to 2. RAM 52 receives the encoded key portion of the message from data selection and buffer amplifier circuit 44 and temporarily stores this key.
Once the appropriate signal is received from comparator 46,
The encoded message in the RAM is sent through gate 50 to the data port of second data decoding circuit 54. The key port of the data decoding circuit 54 is connected to a ROM 56 that contains a hardwired key that is specific to a particular receiver. Accordingly, an encoded new key, the first key, is received at the data port of circuit 54, and a key for decoding such a message is also received from ROM 56 at the key port. Again, circuit 54 may utilize the integrated circuits described above or of similar type and quality. circuit 54
The output from is a new decrypted first key, which is stored in storage 38 so that subsequent data comprising the message can be decrypted.

In summary, the two-tier security system initiated herein utilizes a first key to encode information with a message in digital form. This first key is changed regularly or randomly depending on the security required in the particular communication environment. When there is to be a change in the first key, the new first key is itself encoded in a message specific to each individual receiver or to a subgroup of subscriber receivers as described above. The message includes the receiver's address and a first key encoded with a code unique to that particular receiver.
There is therefore a series of such messages, one for each receiver in the system. At the receiver, the encoded first key is decoded by a second key specific to that receiver. The decrypted first key is then used to decrypt subsequent information comprising the digital message.

While the preferred form of the invention has been illustrated and described, it should be understood that many changes, substitutions and modifications may be made thereto.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a transmitter usable in a system of the type described above according to the invention. Second
The figure is a block diagram of a receiver that can be used with the transmitter of FIG. 1. In these drawings, 10 is a digital audio source, 12 is an audio encoding circuit, 14 is a key generator,
20 is a key change start circuit, 28 is a voice key encoding circuit, 36 is a data decoding circuit, and 54 is a data decoding circuit.

Claims (1)

[Scope of Claims] 1. A transmitter for encoding and broadcasting a digital information-bearing signal, and a subscription system for decoding said encoded digital information-bearing signal to be broadcast to a plurality of subscription television subscribers. a subscription television system comprising: (A) the transmitter; (b) a first changeable key that is common to all subscription television subscribers; (b) new first key means (20) for generating a new first key start signal and causing the first key generating means to generate the changed first key; (c) the digital signal and the changeable first
means (12) connected to receive a key and for encoding the digital signal with the first key to generate a first key encoded digital signal; (d) receiving the new first key start signal; and the first key encoded by the second key
Means (22, 24, 26, 28) for generating an information message comprising a key and an address for each of the plurality of subscription television subscribers, the second key being the address for each of the plurality of subscription television subscribers. being different from each other,
and (e) means (16, 18) for simultaneously broadcasting said first key-encoded digital signal and said information message combined therewith to said plurality of subscription television subscribers; ) the receiver (a) is connected to receive a first key encoded with the second key of the information message and has a subscriber key unique to each subscription television subscriber; a first decoding means (44,
52, 50, 54, 56), and (b) connected to receive the first key encoded digital signal and the decoded first key, and decode the digital signal with the first key. (c) second decoding means (36) for generating a decoded digital signal, and (c) being connected to receive said address portion of said information message and having a predetermined receiver address, said address portion being connected to receive said address portion of said information message; address means (42,
46, 48), a subscription television system comprising: